1. Field of the Invention
The present invention relates to a zoom lens system and an electronic image pickup apparatus using the same.
2. Description of the Related Art
Heretofore, as a zoom lens system for photographing, a zoom lens system including, in order from an object side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power and a fourth lens unit having a negative refractive power has been known.
In the zoom lens system having such a refractive power layout, the lens units (the first and third lens units) having the positive refractive power and the lens units (the second and fourth lens units) having the negative refractive power are alternately arranged: In this zoom lens system, the second and third lens units are main magnification change units, and an off-axial light flux is struck up by the negative power of the fourth lens unit. This constitution is advantageous in reducing a size of the zoom lens system relative to an image surface size. The zoom lens system has a lens unit arrangement in which two telephoto types are arranged, and this constitution is advantageous for reduction of the total length of the zoom lens system.
Moreover, in an image pickup apparatus such as a digital camera or a video camera, an electronic image sensor such as a CCD image sensor or a CMOS image sensor is used as an image pickup element. In the camera in which the electronic image sensor is used, it is preferable to emit a light flux from a photographing lens system so that the light flux is nearly vertical to an image pickup surface of the image sensor (reduce an angle of the light flux with respect to a normal of the image pickup surface). Therefore, an exit pupil of the photographing lens system is disposed far from the image pickup surface. According to such a constitution, an incidence angle of a ray upon the image pickup surface can be inhibited from being excessively enlarged in the peripheral area of the image pickup surface of the image sensor. As a result, decrease of a quantity of light in the peripheral area of an image and deterioration of a color reproduction property are inhibited.
On the other hand, in recent years, there are electronic image sensors that use a technology in which an arrangement of a micro lens disposed right before each pixel is devised with respect to each pixel to improve an oblique incidence property upon the image pickup surface.
The exit pupil is far from the image surface, and the incidence angle of the light flux upon the image pickup surface is close to zero. A zoom lens system including a refractive power layout having positive, negative, positive and negative powers from the object side is disclosed in, for example, Japanese Patent Application Laid-Open Nos. 09-197272 and 04-53916.